Mechanical converters



Dec. 2, 1958 F. .KOPPELMANN 2,363,110

MECHANICAL coNvERTERs original Filed April 15, 195o 2 sheetsfsheel 1 l?IA923 20g 211I -20l A ZL n .WL 20f 202,4" 20F HJM umn Amm Amm Dec. 2,1958 F. KoPPl-:LMANN 2,863,110

MECHANICAL coNvERTERs l original Filed April 15, 195o 2 sheets-sheet 21S B, Sm SN QS @2N .E NN

m J I 1 E 9TH. Nw NN h. NQ Sm n MQ NQ M? @w NQ HQ E United States PatentC) MECHANICAL CNVERTERS Floris Koppelmann, Berlin-Reinickendorf,Germany, as-

signor to Licentia Patent-Verwaltungs, G. m. b. H., Berlin, Germany, acorporation of Germany @riginal application April 13, 1950, Serial No.155,585, now Patent No. 2,666,102, dated January 12, 1954. Divided andthis application ctober 21, 1952, Serial No. 315,893

Claims priority, application Germany November 4, 1949 11 Claims. (Cl.321-48) The present invention relates to an arrangement for convertingalternating current into direct current and more particularly formechanically converting a three-phase current into direct current.

This application is a division of my co-pending application Serial No.155,585, filed April 13, 1950, entitled Mechanical Rectifier, now PatentNo. 2,666,102.

It is an object of the invention to provide an arrangement which has atransformer of simple design and a high output.

lt is another object of the present invention to provide an arrangementcapable of being greatly overloaded.

An arrangement according to the present invention comprises incombination a three-phase transformer having primaries adapted forconnection to a three-phase current supply, and a secondary winding forsupplying a multi-phase current, a plurality of movable contactsconnected, respectively, to the secondary winding so as to be fed,respectively, with the phases of the multi-phase current, a plurality ofpairs of stationary contacts coo-perating, respectively, with themovable contacts, and a D. C. line having a positive and a negativeterminal, one 'of the stationary contacts of each of the pairs beingconnected to the positive terminal, the other of the stationary contactsof each of the pairs being connected to the negative terminal.

In one embodiment of the present invention the secondary winding isformed as la six-phase winding having six junctions connected,respectively, to six phase connections to which movable contacts areconnected, respectively.

Preferably three condensers are connected, respectively, between thephase connections connected to opposite ones of the six junctions.

Preferably choke coils and, if desired, switches Iare arranged,respectively, in the phase connections.

Preferably, the movable contacts move together in pairs.

ln another embodiment of the present invention the transformer hasseparate single phase secondaries which are preferably connected at themidpoint thereof to a common star point through resistances,respectively.

Preferably three chokes are connected, respectively, in series to thesecondaries and three condensers are connected, respectively, in shuntto the series connections of the chokes and the secondaries.

The novel features which are considered as characteristie for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings inwhich:

Fig. 1 is a current diagram for the explanation of the invention;

Fig. 2 is a diagram showing a converting arrangement;

"ice

Fig. 3 is a diagram for the explanation of the operation of thearrangement shown in Fig. 2;

Fig. 4 is a diagram showing another converting arrangement;

Fig. 5 is a diagram similar to Fig. 3 for the explanation of theoperation of the arrangements shown in Fig. 4 and Fig. 6; and

Fig. 6 is a converting arrangement according to the invention.

Referring now to the drawings, and first to Fig. 1, the current 1 isplotted against the time t which flows in a mechanical rectifiercomprising a choke inserted in the alternating current circuit whichflattens the current at the points where it becomes zero so that thecurrent is practically Zero for approximately one millisecond as shownat a in Fig. 1. During this time the contacts of the mechanicalrectifiers are opened and closed. The contacts are moved synchronouslywith th-e alternating current to be converted, for instance by means ofa synchronous motor and eccentrics as more fully described in the parentapplication Serial No. 155,585 mentioned hereinabove. y

Whereas in mercury vapor rectifiers a voltage of l0 to 20 vo-lts isconsumed in the arc, in mechanical rectifiers practically no voltagedro-p is encountered at the contacts so that mechanical rectifiers evenfor small direct voltages can be designed which have a high efficiency.The negligibly small voltage drop at the contacts, which for instanceamounts to ya few millivolts, renders it possible to provide a bridgeconnection instead of the star connection of the transformer which iscustomary in connection with mercury vapor rectifiers. In the bridgeconnection the current to be rectified is twice led over contacts andthe bridge connection involves the advantage that the transformer of therectifier is of simple design and has a high efficiency.

Fig. 2 shows a three-phase bridge connection for mechanical rectifiersinvolving one choke for each phase. In Fig. 2 the three-phase line isconnected to the primary 12 of the transformer which is connected instar. The secondary 14 of the transformer is connected in delta. 1n eachphase connection 16, 161, 1611 is connected, respectively, a switch 18,181, 1811 and a choke 20, 201, 2011, each of which preferably comprisesa single phase winding on an iron core. The switches 18, 181, 1811, canbe single-pole switches which may be coupled with one another.Preferably the switches 18, 181, 1811 are designed as high-speedswitches which rapidly interrupt the current in case of a short circuitbetween the phases. Condensers 22, 221, 2211 are inserted between thephase connections, 16, 161, 1611 and serve for extinguishing any shortcircuit. 24, 26 and 28 are the movable contacts of the rectifiers. Eachof the movable contacts 24, 26, 28 cooperates with a pair of stationarycontacts such as 30 and 32 which are conncted, respectively, to thepositive and to the negative bus bar of the direct current line 34.

The operation of this device is as follows: Each of the contacts 24 to28 is moved between its cooperating stationary contacts synchronously inthe rhythm of the alternating frequency and with a phase differenceamounting to between the actions of the contacts 24 to 28. As will beseen from Fig. 2, when contact 24 is in the position making contact withcontact 30 connected to the positive bus bar, contact 26 is in Contactwith the stationary contact connected to the negative bus bar andContact 2S is in the middle position between its stationary contacts.Each phase connection 16, 161, 1611 is alternately connected to thepositive and negative bus bar of the direct current line 34 and thecontacts 24 to 28 are kept in contact with each cooperating stationarycontact such as 30 and 32 for 120 of the alternating current cycle asshown in Fig. 3. This period of 120 is followed transformer which isconnected in delta.

by 60 during which the phase connection 16 does not carry any current.After that the contact such as 24 makes Contact with the otherstationary contact connected to the negative bus bar again for 120 whichis followed again by 60 during which no current flows, etc. Thus it willbe seen that with this connection the chokes 20,

201, 2011 are traversed by currents for 120 whereas the reduced by thefact that the chokes have to be kept small.

For this reason a six-phase bridge connection instead of a three-phaseone is used such as shown in Fig. 4 of the drawings. In this gure athree-phase alternating current line 10 is connected to the primary 12of the The secondary 14 of the transformer is designed as a six-phasewinding the junctions of which are connected, respectively, to phase oranode connections 16, 161 16V, each having a switch 18, 181 18V and achoke 20, 201 .2011. The condensers 22, 221, 2211 are each connectedbetween the phase connections such as 16 and 16111 starting fromopposite points of the secondary 14. Each phase connection 16 to 16V isconnected to a movable Contact 24, 24', 26, 26', 28, and 28 which movesbetween the stationary contacts, such as 30 and 32, connected,respectively, to the positive and to the negative bus bar of the directcurrent line 34. The movable contacts 24 and 24 move together and thesame holds for the movable contacts 26 and 26', and 28 and 28'. Themovable contacts are controlled so that the current in each phaseconnection 16 to 16V is closed for a time equivalent to 60 of a cycle inone direction and to 60 in the opposite direction these periods beingseparated from each other by an interval of 120 during which no currentflows in the phase connection, as shown in Fig. of the drawings. By thismeans suticient time is gained for commutating the current so that therectiers are simpler to operate and the safety against short circuits isincreased. The disadvantage of this device is that a six-pole switch 18,181 etc., and six chokes 20, 201 etc., are required and that thetransformer is more complicated because its secondary 14' has to bedesigned as a six-phase winding.

The invention overcomes this drawback by using a much simpler six-phaseconnection which is shown in Fig. 6.

In Fig. 6, is again the three-phase A. C. line and 12 thedelta-connected primary of the transformer which is connected to thethree-phase A. C. line 10. The secondary of the transformer comprisesthree single phase windings 14a, 14b, 14C cooperating, respectively,with the windings of the delta-connected primary 12. The mid points 36a,36b and 36e of the secondaries 14a, 1417, and 14e are connected,respectively, to one terminal of preferably equal high-ohmic resistances37a, 37b, and 37e, respectively, the other terminals of which areconnected to a common star point 38. The terminals of secondary 14a areconnected, respectively, to the phase connections 16 and 16111, theterminals of secondary 14h to the phase connections 1611 and 16V, andthe terminals of secondary 14e to the phase connections 161 and 161V. Inphase connection 16 a switch 18 and a choke 20 are inserted, in phaseconnection 161 a switch 181 and a choke 201 and in phase connection 1611a switch 1811 and a choke 2011 are inserted. After the interconnectedswitches and chokes, the phase connections 16 and 16111 are bridged by acondenser 221, phase connections 1611 and 16V by a condenser 22, andphase connections 161 and For instance, the

161V by a condenser 2211. Each phase connection 16, 161 etc., ends intwo branches such as 16a and 16b, 161:1 and 161b etc., leading tostationary contacts such as 30 and 32. It will be seen from Fig. 6 thattwelve such stationary contacts are provided. Associated with eachstationary contact is another stationary contact such as 30a, 32a etc.,being arranged on the same level. The contacts 30a and 32a areconnected, respectively, to the positive and to the negative bus bar ofthe D. C. line 34, and so on for the other contacts. Movable contactbridges 40, 42 60, 62 are arranged to bridge the stationary contacts 30,30a, 32, 32a etc. As will be seen from Fig. 6 the bridges 40 and 46 areat a certain moment in contact with their stationary contacts whereasthe other bridges are at this moment not in contact with theirstationary contacts but separated from them by different distances asmore fully described in the parent application Serial No. 155,585mentioned hereinabove, and particularly Fig. 4 thereof. Each contactbridge such as 40 is connected to a rod such as 64 which is operatedupon by an eccentric such as 66 through a pivoted lever such as 68; theeccentrics are arranged on a common shaft 70 which is driven by athree-phase motor 72 synchronously with the three-phase current to beconverted. The motor '72 is preferably connected to the line 10 carryingthe three-phase A. C. current to be converted. The design of the bridges40 to 62 and the driving mechanism thereof is more fully described indetail in connection with Fig. 4 of the parent application Serial No.155,585 mentioned hereinabove. It should be understood, however, that ata certain instant the bridge 40 connects the phase connection 16 to thepositive bus bar of the direct current line 34 and the bridge 46connects the phase connection 16111 to the negative bus bar, whereas thebridges 42 and 44 belonging to the other end branches of the phaseconnections 16, 16111 are in their position farthest apart from thestationary contacts. The other bridges are in certain mean positions notquite so far apart from their stationary contacts as bridges 42 and 44,and the eccentrics 66 etc. are so arranged on the common shaft '70 thateach phase connection 16 etc. is connected to a bus bar of the directcurrent line 34 for a time period equivalent to 60 of a cycle of the A.C. current followed by during which the respective phase connection doesnot carry any current. ln consequence thereof the current diagram shownin Fig. 5 holds also for Fig. 6. But the arrangement shown in Fig. 6 issimpler than that shown in Fig. 4 in that the transformer has not asix-phase secondary winding and that the switches 1S, etc. and chokes20, etc. are only provided three-fold instead of six-fold as in Fig. 4.

The star point 38 which has been created by means of the high-ohmicresistances 37a, 37b, and 37C serves to control the potentials of thethree phases during the in` tervals in which they do not carry anycurrent.

The arrangement shown in Fig. 6 requires twelve movable contact bridgeswhich, however, involves a disadvantage only at small outputs. Owing tothe greater time period available for commutating the current (120instead of 60) larger currents can be recited. The voltage at thecontacts is, with equal direct line voltage, only half as much as with athree-phase connection so that with a six-phase connection twice thevoltage, for instance 800 volts, can be generated as compared withthree-phase connections. Thus it is seen that with the six-phaseconnection the units may be designed for much higher powers so that inlarge plants the number of movable contacts is smaller with a six-phaseconnection than with a three-phase connection in which several smallunits have to be connected in parallel or in series.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofarrangement for converting alternating current into direct currentdiiering from the types described above.

While I have illustrated and described the invention as embodied in anarrangement for mechanically con- Verting three-phase current intodirect current, I do not intend to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of my invention.

Without further analysis, the foregoing will so fully reveal the gist ofmy invention that others can by applying current knowledge readily adaptit for various applications without omitting features that, from thestandpoint of prior art, fairly constitute essential characteristics ofthe generic or speciiic aspects of this invention.

What l claim as new and desire to secure by Letters Patent is:

l. An arrangement for mechanically converting an alternating currentinto direct current comprising, in combination, a transformer havingprimary windings connected in polyphase and secondary windings connectedin single phase, each of said secondary windings respectively having twoopposite end terminals; electrical impedance means connected in circuitwith at least a portion of each of said secondary windings to form asix-phase bridge connection; a plurality of pairs of switches, each ofsaid switches being movable between circuit opening position and circuitclosing position, each of said end terminals of said secondary windingsbeing respectively connected to one side of a different pair of saidplurality of pairs of switches; a plurality of saturable reactors, eachof said reactors being connected respectively, between one of said endterminals of each of said secondary windings and its respective pair ofswitches; means for moving each of said switches between circuit openingand circuit closing positions in synchronism with said alternatingcurrent to be rectied and the respective phase position of the secondarywinding to which the respective switch is connected, one of saidswitches of each of said pairs of switches being moved into circuitclosing position when the other switch of its respective pair is incircuit opening position and vice versa; a pair of direct current outputterminals; and means for connecting the other side of one switch of eachof said pairs of switches to one of said output terminals and the otherside of the other switch of said pairs of switches to said other outputterminal.

2. An arrangement for mechanically converting a threephase current intodirect current comprising,'in combination, a transformer having threeprimary windings connected in polyphase and three secondary windingsconnected in single phase, each of said secondary windings respectivelyhaving two opposite end terminals; electrical impedance means connectedin circuit with at least a portion of each of said secondary windings toform a sixphase bridge connection; a plurality of pairs of switches,each of said switches being movable between circuit opening position andcircuit closing position, each of said end terminals of said secondarywindings being respectively connected to one side of a diierent pair ofsaid plurality of pairs of switches; three saturable reactors, each ofsaid three reactors being connected respectively, between one of saidend terminals of each of said secondary windings and its respective pairof switches; means for moving each of said switches between circuitopening and circuit closing positions in synchronism with saidthree-phase current to be rectified and the respective phase position ofthe secondary winding to which the respective switch is connected, oneof said switches of each of said pairs of switches being moved intocircuit closing position when the other switch of its respective pair isin circuit opening position and vice versa; a pair of direct currentoutput terminals; and means for connecting the other side of one switchof each of said pairs of switches to one of said output terminals andthe other side of the other switch of said pairs of switches to saidother output terminal. v

3. A arrangement for mechanically converting an alternating current intodirect current comprising, in combination, a transiormer having primarywindings connected in polyphase and secondary windings connected insingle phase, each of said secondary windings respectively having twoopposite end terminals; electrical impedance means connected in circuitwithat least a portion of each of said secondary windings to form asix-phase bridge connection; a plurality otpairs olf switches, each ofsaid switches being movable between circuit opening position and circuitclosing position, each of said end terminals of said secondary windingsbeing respectively connected to one side of a dilerent pair of saidplurality of pairs of switches; a plurality of saturable reactors, eachof said reactors being connected respectively, between `one of said endterminals of each of said secondary windings and its respective pair ofswitches; a group of capacitors, each of said capacitors beingrespectively connected between the two pairs of switches connected tothe same one of said secondary windings; means for moving each of saidswitches between circuit opening and circuit closing positions insynchronism with said alternating current to be rectiiied and therespective phase position of the secondary winding to which therespective switch is connected, one of said switches of each of saidpairs of switches being moved into circuit closing position when theother switch of its respective pair is in circuit opening position andvice versa; a pair of direct current output terminals; and means forconnecting the other side of one switch of each of said pairs ofswitches to one of said output terminals and the other side of the otherswitch of said pairs of switches to said other output terminal.

4. An arrangement for mechanically converting a threephase current intodirect current comprising, in combination, a transformer having threeprimary windings connected -in polyphase and three secondary windingsconnected in single phase, each of said secondary windings respectivelyhaving two opposite end terminals; electrical impedance means connecte-din circuit with at least a portion of each of said secondary windings toform a six-phase bridge connection; a plurality of pairs of switches,each of said switches being movable between circuit opening position andcircuit closing position, each of said end terminals of said secondarywindings being respectively connected to one side of a different pair ofsaid plurality of pairs of switches; three saturable reactors, each ofsaid three reactors being connected respectively, between one of saidend terminals of each of said secondary windings and its respective pairof switches; a group of capacitors, each of said capacitors beingrespectively connected between the two pairs of switches connected tothe same one of said secondary windings; means for moving each of saidswitches 'between circuit opening and circuit closing positions insynchronism with said three-phase current to be rectifier and therespective phase position of the secondary winding to which therespective switch is connected, one of said switches of each of saidpairs of switches being moved into circuit closing position when theother switch of its respective pair is in circuit opening position andvice versa; a pair of direct current output terminals; and means forconnecting the other side of one switch of each of said pairs ofswitches to one of said output terminals and the other side of the otherswitch of said pairs of switches to said other output terminal.

5. An arrangement for mechanically converting an alternating currentinto direct current comprising, in combination, a transformer havingprimary windings connected in polyphase and secondary windings connectedin single phase, each of said secondary windings respectively having twoo-pposite end terminals; a set of resistors, each of said resistorshaving a substantially high resistance which is equal to the resistanceof the other resistors, each of said resistors also being respectivelyconnected between the midpoint of one of said secondary windings and acommon junction point of said resistors 7 to form a six-phase bridgeconnection; a plurality of pairs of switches, each of said switchesbeing movable between circuit opening position and circuit closingposition, each of said end terminals of said secondary windings beingrespectively connected to one side of a diterent pair of said pluralityof pairs of switches; a plurality of saturable reactors, each of saidreactors being connected respectively, between one of said end terminalsof each of said secondary windings and its respective pair of switches;means for moving each of said switches between circuit opening andcircuit closing positions in synchronism with said alternating currentto be rectified and the respective phase position of the secondarywinding to which the respective switch is connected, one of saidswitches of .each of said pairs of switches being moved into circuitclosing position when the other switch of its respective Vpair is incircuit opening position and vice versa; a pair of direct current outputterminals; and means for connecting the other side of one switch of eachof said pairs of switches to one of said output terminals and the otherside of the other switch of said pairs of switches to said other outputterminal.

6. An arrangement for mechanically converting a threephase current intodirect current comprising, in combination, a transformer having threeprimary windings connected in polyphase and three secondary windingsconnected in single phase, each of said secondary windings respectivelyhaving two opposite end terminals; a set of resistors, each of saidresistors having a substantially high resistance which is equal to theresistance of the other resistors, each of said resistors also beingrespectively connected between the midpoint of one of said secondarywindingsand a common junction point of said resistors to form asix-phase bridge connection; a plurality of pairs of switches, each ofsaid switches being movable between circuit opening position and circuitclosing position, each of said end terminals of said secondary windingsbeing respectively connected to one side of a different pair of saidplurality of pairs of switches; three saturable reactors, each of saidthree reactors being connected respectively, between one of said endterminals of each of said secondary win-dings and its respective pair ofswitches; means for moving each of said switches between circuit openingand circuit closing positions in synchronism with said three-phasecurrent to be rectified and the respective phase position of thesecondary winding to which the respective switch is connected, one ofsaid switches of each of said pairs of switches being moved into circuitclosing position when the other switch of its respective pair is incircuit opening position and vice versa; a pair of direct current outputterminals; and means for connecting the other side of one switch of eachof said pairs of switches to one of said output terminals and the otherside of the other switch of said pairs of switches to said other outputterminal.

7. An arrangement for mechanically converting an alternating currentinto direct current comprising, in ccmbination, a transformer havingprimary windings connected in polyphase and secondary windings connectedin single phase, each of said secondary windings respectively having twoopposite end terminals; a set of resistors, each of said resistorshaving a substantially high resistance whichis equal to the 'resistanceof the other resistors, each of said resistors also being respectivelyconnected between the midpoint of one of said secondary windings and acommon junction point of said resistors to form a six-phase bridgeConnection; a plurality of pairs of switches, each of said switchesbeing movable between circuit opening position and circuit closingposition each of said end terminals of said secondary windings beingrespectively connected to one side of a different pair of said pluralityof pairs of switches; a plurality of saturable reactors, each of saidreactors being connected respectively, between one of said end terminalsof each of said secondary windings and its respective pair of switches;

a group of capacitors, each of said capacitors being respectivelyconnected between the two pairs of switches connected to the same one ofsaid secondary windings; means for moving each of said switches betweencircuit opening and circuit closing positions in synchronism with saidalternating current to be rectied and the respective phase position ofthe secondary winding to which the respective switch is connected, oneof said switches of each of said pairs of switches being moved intocircuit closing position when the other switch of its respective pair isin circuit opening position and vice versa; a pair of direct currentoutput terminals; and means for connecting the other side of one switchof each of said pairs of switches to one of said output terminals andthe other side of the other switch of said pairs of switches to saidother output terminal.

8. An arrangement for mechanically converting an alternating currentinto direct current comprising, in combination, a transformer havingprimary windings connected in polyphase and secondary windings connectedin single phase, each of said secondary windings respectively having twoopposite end terminals; electrical impedance means connected in circuitwith at least a portion of each of Said secondary windings to form asix-phase bridge connection; a plurality of pairs of switches, each ofsaid switches being movable between circuit opening position and circuitclosing position, each of said end terminals of said seco-ndary windingsbeing respectively connected.

to one side of a different pair of said plurality of pairs of switches;a plurality of saturable reactors, each of said reactors being connectedrespectively, between one of said end terminals of each of saidsecondary windings and its respective pair of switches; a plurality ofoverload circuit breakers, each of said circuit breakers beingrespectively connected in circuit between one of said saturable reactorsand its respective end terminal for opening the circuit of itsrespective secondary winding in the event of an overload of currenttherein; means for moving each of said switches between circuit openingand circuit closing positions in synchronism with said alternatingcurrent to be rectified and the respective phase position of thesecondary winding to which the respective switch is connected, one ofsaid switches of each of said pairs of switches rbeing moved intocircuit closing position when the other switch of its respective pair isin circuit opening position and vice versa; a pair o-f direct currentoutput terminals; and means for connecting the other side of one switchof each of said pairs of switches to one of said output terminals andthe other side of the other switch of said pairs of switches to saidother output terminal.

9. An arrangement for mechanically converting an alternating currentinto direct current comprising, in coinbinatlon, a transformer havingprimary windings connected in polyphase and secondary windingsconnec-ted 1n single phase, each of said secondary windings respectivelyhaving two opposite end terminals; a set of resistors, each of saidresistors having a substantially high resistance which is equal to theresistance of the other resistors, each of said resistors also beingrespectively connected between the midpoint of one of said secondarywindings and a common junction point of said resistors to form asix-phase bridge connection; a plurality of pairs of switches, each ofsaid switches being movable between circuit opening position and circuitclosing position, each of said end terminals of said seco-ndary windingsbeing respectively connected to one side of a different pair of saidplurality of pairs of switches; a plurality of saturable reactors, eachof said reactors being connected respectively, between one of said endterminals of each of said secondary windings and its respective pair ofswitches; a group of capacitors, each of said capacitors beingrespectively connected between the two pairs of switches connected tothe same one of said secondary windings; a plurality of overload circuitbreakers, each of said circuit breakers being respectively connected incircuit between one of said saturable reactors and its respective endterminal for opening the circuit of its respective secondary winding inthe event of an overload of current therein; means for moving each ofsaid switches between circuit opening and circuit closing positions insynchronism with said alternating current to be rectied and therespective phase position of the `secondary winding to which therespective switch is connected, one of said switches of each of saidpairs of switches being moved into circuit closing position when theother switch of its respective pair is in circuit opening position andvice versa; a-pair of direct current output terminals; and means forconnecting the other side of one switch of each of said pairs ofswitches to one of said output terminals and the other side of the otherswitch of said pairs of switches to said other output terminal.

10. An arrangement for mechanically converting an alternating currentinto direct current comprising, in combination, a transformer havingprimary windings connected in delta connection and secondary windingsconnected in single phase, each of said secondary windings respectivelyhaving two opposite end terminals; electrical impedance means connectedin circuit with at least a portion of each of said secondary windings toform a six-phase bridge connection; a plurality of pairs of switches,each of said switches being movable between circuit opening position andcircuit closing position, each of said end terminals of said secondarywindings being respectively connected to one side of a different pair ofsaid plurality of pairs of switches; a plurality of saturable reactors,each of said reactors being connected respectively, between one of saidend terminals of each of said secondary windings and its respective pairof switches; means for moving each of said switches between circuitopening and circuit closing positions in synchronism with saidalternating current to be rectified and the respective phase position ofthe secondary winding to which the respective switch is connected, oneof said switches of each of said pairs of switches being moved intocircuit closing position when the other switch of its respective pair isin circuit opening position and vice versa; ya pair of direct currentoutput terminals; and means for connecting the other side of one switchof each of said pairs of switches to one of said output terminals andthe other side of the other switch of said pairs of switches to saidother output terminal.

11. An arrangement for mechanically converting a three-phase currentinto direct current comprising, in combination, a transformer havingthree primary windings connected in delta connection and three secondarywindings connected in single phase, each of said secondary windingsrespectively having two opposite end terminals; a set of resistors, eachof said resistors having a substantially high resistance which is equalto the resistance of the other resistors, each of said resistors alsobeing respectively connected between the midpoint of one of saidsecondary windings and a common junction point of said resistors to forma six-phase bridge connection; a plurality of pairs of switches, Ieachof said switches being movable between circuit opening position andcircuit closing position, each of said end terminals of said secondarywindings being respectively connected to one side of a dilerent pair ofsaid plurality of pairs of switches; three saturable reactors, each ofsaid three reactors being connected respectively, between one of saidend terminals of each of said secondary windings and its respective pairof switches; a group of capacitors, each of said capacitors beingrespectively connected between the two pairs of switches connected tothe same one of said secondary windings; means for moving each of saidswitches between circuit opening and circuit closing positions insynchronism with said threephase current to be rectied and therespective phase position of the secondary winding to which therespective switch is connected, one of said switches of each of saidpairs of switches being moved into circuit closing position when theother switch of its respective pair is in circuit opening position andvice versa; a pair of direct current output terminals; and means forconnecting the other side of one switch of each of said pairs ofswitches to one of said output terminals and the other side of the otherswitch of said pairs of switches to said other output terminal.

References Cited in the le of this patent UNITED STATES PATENTS2,179,337 Leukert Nov. 7, 1939 2,310,792 Koppelmann et al. Feb. 9, 19432,697,198 Schmidt et al. Dec. 14, 1954 FOREIGN PATENTS 217,879Switzerland June 16, 1942 723,928 Germany Aug. 13, 1942 877,414 FranceDec. 7, 1942

